On Mon, Dec 28, 2015 at 04:35:46PM +0100, Arnd Bergmann wrote: > On Monday 28 December 2015 10:20:56 Thierry Reding wrote: > > > > > HTC apparently uses a separate RAM area to pass the reboot reason, > > > > > and they have a driver to store that, which is separate from the > > > > > driver that they use for actually rebooting the machine. > > > > > > > > I wasn't very clear, but the PMC_SCRATCH0 register is used to store the > > > > reset reason. It supports the recovery mode, which I think is really an > > > > Android thing, "bootloader" will typically cause the bootloader not to > > > > boot anything, and "forced-recovery" will go into a recovery mode that > > > > is used to bootstrap the device (usually by uploading a "miniloader" > > > > that initializes RAM, downloads a bootloader for booting or flashing an > > > > operating system, ...). > > > > > > > > The write that resets the SoC is to a different register. > > > > > > So is this scratch register interpreted by some maskrom code, or by code that > > > can be provided by the OEM? > > > > My understanding is that its interpreted both by what's called BootROM > > on Tegra (I guess that's what you call "maskrom code") and the system's > > bootloader. The BootROM cannot typically be replaced by the OEM, but it > > is quite typical for the bootloader to differ between devices. > > Ok, so not maskrom (which would not be OEM specific, but hardcoded for > the chip) but rather some form of PROM. This means we can only guess > that all OEMs use the same protocol but in theory someone could have > implemented an incompatible BootROM, but it's also possible that HTC > just ignore the register entirely and implement the same thing separately. I wasn't being clear, the BootROM is hardcoded for the chip, I'm not aware of a way to replace it once the chip's taped out. Thierry
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